Lamination molding apparatus

ABSTRACT

A lamination molding apparatus includes a chamber, covering at least a molding area which is the maximum range in which a three-dimensional object can be produced; a molding table, disposed in the molding area in the chamber, on which material powder layers are formed by uniformly spread material powder for each of divided layers, wherein the divided layers are obtained by dividing a desired three-dimensional object for each of a specific thickness; a powder holding wall, surrounding the molding table and holding the material powder supplied onto the molding table; a laser irradiation device, forming sintered layers by irradiating laser beam on specific irradiation areas defined by the contour shape of the desired three-dimensional object of the divided layers on the material powder layers; and a numerical control device, determining, at least before sintering, whether the irradiation areas of all the divided layers are included in the molding area.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japanese PatentApplication No. 2016-171051, filed on Sep. 1, 2016. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a lamination molding apparatus.

2. Description of Related Art

In the selective laser sintering method using laser beam, materialpowder is uniformly spread on a molding table to form a material powderlayer. Next, the laser beam is irradiated on a specific portion of thematerial powder layer to form a sintered layer. Furthermore, materialpowder is then uniformly spread on the sintered layer to form a newmaterial powder layer. Then, the laser beam is irradiated on the newmaterial powder layer to sinter the material powder so as to form a newsintered layer that is bonded with the lower sintered layer. Byrepeating these steps, a desired three-dimensional object that is unitedas a sintered body formed by laminating a plurality of sintered layersis obtained.

The laser beam is scanned by an optical deflector, for example, agalvano scanner. Due to the displacement of the optical deflector or theapparatus, an unavoidable deviation occurs between a specific scanningpath on the laser control device and a scanning track actually formed onthe material powder layer. Therefore, to enable the laser beam to beirradiated along a specific scanning path, the deviation amount must bemeasured and corrected. For example, as disclosed in Patent Document 1(Japanese Patent No. 2979431) and Patent Document 2 (Japanese Patent No.3446741), a lamination molding apparatus that is well known uses amethod as follows to measure the deviation amount and correct thedeviation. Specifically, a calibration plate such as a plate or thermalpaper that is disposed on a molding area is scanned in a grating frameshape at regular intervals with the laser beam, specific positions suchas intersections of the scanning track are measured, and the actualirradiated positions of the laser beam toward the specific positions arecompared with reference positions.

In addition, for safety purpose, in a lamination molding apparatus usinglaser beam has limits with regard to the irradiation position of thelaser beam. The limits are a mechanical limit which is a physical limitand a software limit which is a control limit, so that anirradiation-enabled area, which is an area that allows irradiation ofthe laser beam, can be set by the limits. In another aspect, as in theinventions of Patent Document 1 and Patent Document 2, when thedeviation amount is measured and the scanning path or a plurality ofirradiation positions is corrected with reference to a molding area,that is, the largest area in which a three-dimensional object can beproduced, a correction area which includes the scanning track of thelaser beam in the grating frame shape or a plurality of irradiationmarks formed before the correction may partially exceed the moldingarea. Therefore, in order to correctly perform the correction, it isnecessary to set the irradiation-enabled area to include the moldingarea and to be larger than the molding area on control.

SUMMARY OF THE INVENTION

In a lamination molding apparatus in which the irradiation-enabled areais set to include a molding area and to be larger than the molding area,in case of a mistake in molding data which contains a command forirradiating an area outside the molding area, laser beam is irradiatedoutside the molding area so that the object cannot be produced normally,and the apparatus may be damaged. Even if the irradiation-enabled areais set to be as large as the molding area, when the original moldingdata has errors, the molding cannot be continued, so the material powderconsumed so far is wasted, and time is wasted.

In view of this, the present invention is accomplished to provide alamination molding apparatus, which can properly form athree-dimensional object in a molding area by determining before moldingwhether an irradiation area of laser beam of all divided layers isincluded in the molding area.

According to the present invention, a lamination molding apparatus isprovided, including a chamber, covering at least a molding area which isthe maximum range in which a three-dimensional object can be produced; amolding table, disposed in the molding area in the chamber, on whichmaterial powder layers are formed by uniformly spread material powderfor each of a plurality of divided layers, wherein the divided layersare obtained by dividing a desired three-dimensional object for each ofa specific thickness; a powder holding wall, surrounding the moldingtable and holding the material powder supplied onto the molding table; alaser irradiation device, forming sintered layers by irradiating laserbeam on specific irradiation areas defined by the contour shape of thedesired three-dimensional object of the divided layers on the materialpowder layers; and a numerical control device, determining, at leastbefore sintering, whether the irradiation areas of all the dividedlayers are included in the molding area.

In the lamination molding apparatus of the present invention, themolding starts after whether the irradiation areas of the laser beam isincluded in the molding area in all the divided layers is determined.Therefore, the three-dimensional object can be properly formed withinthe molding area, so that the molding interruption can be prevented. Inaddition, the damage to the apparatus caused by the laser beamirradiated on improper positions can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of a lamination molding apparatus 1according to an embodiment of the present invention.

FIG. 2 is a perspective view of a powder layer forming device 3 and alaser irradiation device 5.

FIG. 3 is a perspective view of a recoater head 4.

FIG. 4 is a perspective view of the recoater head 4 viewed from anotherangle.

FIG. 5 is a top view of a molding table 33, a powder holding wall 35,and an upper wiper 37, and illustrates a coordinate system of thelamination molding apparatus 1.

FIG. 6 is a block diagram of a control system of the lamination moldingapparatus 1.

FIG. 7 is a diagram illustrating an example of a method for generating acutting path when a cutting tool 212 cuts an upper surface.

FIG. 8 is a diagram illustrating the example of the method forgenerating the cutting path when the cutting tool 212 cuts the uppersurface.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings in the following. Modifications to a plurality ofconstituent members described in the following can be freely combinedand implemented.

As shown in FIG. 1, a lamination molding apparatus 1 according to anembodiment of the present invention includes a substantially sealedchamber 10. The chamber 10 is separated into a molding compartment 11and a drive compartment by bellows. A powder layer forming device 3 isdisposed in the molding compartment 11 in which the lamination moldingis performed. The drive compartment accommodates most part of aprocessing head drive device 23. In FIG. 1, only the molding compartment11 is shown. An inactive gas supply device (not shown) supplies aninactive gas to the molding compartment 11 and the drive compartment ina manner that the chamber 10 is constantly filled with the inactive gasabove a specific concentration, and discharges the inactive gascontaminated by fume generated due to the irradiation of laser beam Lout of the chamber 10. In addition, in this specification, the inactivegas is a gas that does not substantially react with the material powder,for example, nitrogen gas, argon gas, and helium gas, which may beselected according to the type of the material powder.

The powder layer forming device 3 includes a base table 31 having amolding area α, and includes a recoater head 4 disposed on the basetable 31 and configured to be movable along a horizontal uniaxialdirection (a direction indicated by arrows S). A molding table 33movable along a vertical direction (a direction indicated by arrows U)is disposed in the molding area α. When the lamination molding apparatus1 is used, a molding plate 61 is arranged on the molding table 33, and amaterial powder layer 63 is formed on the molding plate 61. A powderholding wall 35 surrounds the molding table 33. Material powder that hasnot been sintered is held in a powder holding space surrounded by thepowder holding wall 35 and the molding table 33. The molding area α isthe whole of a working area where the molding is performed, that is, thelargest area in which the material powder layer 63 can be formed to formthe sintered layer and in which the three-dimensional object can beproduced, and is substantially equivalent to the entire upper surface ofthe molding table 33.

As shown in FIG. 2, the molding table 33 does not directly contact thepowder holding wall 35. Instead, the upper wiper 37 disposed on theperiphery of the molding table 33 contacts the powder holding wall 35.Moreover, when the molding table 33 moves, the upper wiper 37 slides onthe powder holding wall 35. This structure inhibits leakage of thematerial powder in the powder holding space.

As shown in FIGS. 3 and 4, the recoater head 4 includes a materialstorage portion 41 for storing the material powder, a material supplyportion 43 disposed on an upper surface of the material storage portion41 and serving as a receiving port of the material powder, and amaterial discharge portion 45 disposed on a bottom surface of thematerial storage portion 41 and discharging the material powder in thematerial storage portion 41. The material discharge portion 45 has aslit shape extending in a horizontal uniaxial direction (a directionindicated by arrows T) orthogonal to a movement direction (a directionindicated by arrows S) of the recoater head 4. The material powder is,for example, metal powder such as iron powder in a spherical shapehaving an average particle diameter of 20 μm. In addition, a pair ofblades 47 and 49 are disposed on two side surfaces of the recoater head4, respectively. The blades 47 and 49 planarize the material powderdischarged from the material discharge portion 45 to form the materialpowder layer 63.

The cutting device 2 includes a processing head 21 and a processing headdrive device 23. The processing head drive 23 includes a Y-axis drivedevice 232, an X-axis drive device 231 and a Z-axis drive device 233.The Y-axis drive device 232 drives the processing head 21 disposed inthe molding compartment 11 to move along a Y-axis direction, the X-axisdrive device 231 drives the Y-axis drive device 232 to move along anX-axis direction, and the Z-axis drive device 233 drives the processinghead 21 to move along a Z-axis direction. The processing head 21includes a spindle head 211. The spindle head 211 is configured so thata cutting tool 212 such as an end mill can be installed on the spindlehead 211 and can rotate about an R axis. With this configuration, theprocessing head 21 can move the spindle head 211 to any position in themolding compartment 11 to perform cutting processing on the sinteredlayer, especially an end surface of the sintered layer. In thefollowing, this cutting processing is referred to as end surfacecutting. The cutting tool 212 may be used to perform cutting processingon the sintered layers every time a specific number of sintered layersare formed. Moreover, to smoothen the sintered layers or the moldingplate 61, the upper surfaces of the sintered layers or the molding plate61 may be cut. In the following, this cutting processing is referred toas upper surface cutting. For example, the upper surface cutting is usedto remove protrusions when the recoater head 4 collides with theprotrusions on the sintered layers.

A laser irradiation device 5 is disposed above the chamber 10. The laserbeam L output from the laser irradiation device 5 is transmitted througha window 13 provided in the chamber 10, and is irradiated on a specificirradiation area β on the material powder layer 63 formed in the moldingarea α, thereby forming the sintered layer. The specific irradiationarea β is included in the molding area α, and is approximatelyconsistent with an area surrounded by the contour shape of the desiredthree-dimensional object. The laser irradiation device 5 can beconstructed to scan the laser beam L two-dimensionally in the moldingarea α. For example, as shown in FIG. 2, the laser irradiation device 5includes a laser beam source 51 for generating the laser beam L, a focuscontrol unit 53 for focusing the laser beam L output by the laser beamsource 51 and adjusting the laser beam L to a desired spot diameter, anda pair of galvanometer mirrors to scan the laser beam Ltwo-dimensionally in the molding area α, that is, an X-axis galvanometermirror 55 and a Y-axis galvanometer mirror 57. The X-axis galvanometermirror 55 and the Y-axis galvanometer mirror 57 rotate with an A axisand a B axis as drive axes respectively, and the laser beam L is scannedalong the X axis direction and the Y axis direction respectively (moreprecisely, XL axis direction and the YL axis direction). The type of thelaser beam L is not limited herein, as long as it can sinter thematerial powder. For example, the laser beam L may be CO₂ laser, fiberlaser, YAG laser. The window 13 is formed by a material that allows thelaser beam L to transmit. For example, when the laser beam L is fiberlaser or YAG laser, the window 13 may be made of quartz glass.

A fume diffusion device 15 covering the window 13 is disposed on theupper surface of the chamber 10. The fume diffusion device 15 includes acylindrical casing 151 and a cylindrical diffusion member 152 disposedin the casing 151. An inactive gas supply space 153 is disposed betweenthe casing 151 and the diffusion member 152. In addition, an opening 154is arranged in the bottom surface of the casing 151 to the inner side ofthe diffusion member 152. A plurality of fine holes 155 is arranged inthe diffusion member 152, so that clean inactive gas supplied from theinactive gas supply device to the inactive gas supply space 153 fills aclean compartment 156 through the fine holes 155. Then, the cleaninactive gas filling the clean compartment 156 is sprayed out throughthe opening 154 towards under the diffusion device 15. The fumediffusion device 15 prevents the window 13 from being contaminated bythe fume generated when the sintered layers are formed, and removes thefume that may traverse the irradiation path of the laser beam L towardsside plates of the chamber 10.

Here, with reference to FIG. 5, a coordinate system of the laminationmolding apparatus 1 according to this embodiment is described. Themachine coordinate system is an inherent coordinate system of thelamination molding apparatus 1. The origin of the machine coordinatesystem is set to a machine origin O_(M), and the coordinate valuethereof is set to (0, 0). The planar coordinate axes of the machinecoordinate system are set to an X axis and a Y axis separately. The workcoordinate system is a reference coordinate system referring to cuttingprocessing, in which the origin is set to a work origin O_(W), and thecoordinate axes are set to an XW axis and a YW axis parallel to the Xaxis and the Y axis respectively. The work origin O_(W) is set as aposition moved from the machine origin O_(M) by an X-axis work offsetvalue X_(W) and a Y-axis work offset value Y_(W) along the X-axisdirection and the Y-axis direction respectively, and the coordinatevalue of the work origin O_(W) is set to (X_(W), Y_(W)). That is, thework offset values X_(W), Y_(W) are compensation values for thedifference between the work origin O_(W) and the machine origin O_(M).The work origin O_(W) is the origin to be used to determine a cuttingposition of the cutting tool 212. By inputting specific work offsetvalues X_(W), Y_(W), a work coordinate system with any position as thework original O_(W) may be defined, thereby implementing molding at adesired position. In other words, the coordinate axes XW and YW in thework coordinate system may be substituted by the X axis and Y axis, sothat the work coordinate system can be controlled as an XY coordinatesystem.

Moreover, the laser coordinate system is a reference coordinate systemreferring to irradiation of the laser beam, in which the origin is setto a laser origin O_(L), and the coordinate axes are set to an XL axisand a YL axis parallel to the X axis and the Y axis respectively. Thework coordinate system is associated with the laser coordinate system,and the laser coordinate system may also be controlled as an XY systemhaving coordinate axes of the X axis and the Y axis. In addition, themolding area α is consistent in various coordinate systems. The laserorigin O_(L), which is the origin of the laser coordinate system, is atthe center of the molding area α, and the coordinate value of the laserorigin O_(L) is set to (X_(L), Y_(L)).

As described above, in the laser coordinate system, in order to enablethe scanning of the laser beam L to irradiate on a specific scanningpath, it is necessary to measure the deviation amount and performcorrection. Therefore, for example, a calibration plate is disposed onthe molding table 33 before the molding starts, and is scanned with thelaser beam L along a specific scan pattern such as a grating frameshape, and specific positions such as intersections of the scanning aremeasured to calculate the deviation amount and correct the deviation.Further, the work coordinate system must be associated with the lasercoordinate system. Therefore, for example, a pair of imaging units (notshown) are arranged opposite to each other with the molding area αtherebetween. Before or during the molding, the laser beam L isirradiated on a central position of the imaging units, so as to measurethe deviation amount from the central position between the imaging unitsto the actual irradiation position and correct the deviation.

Here, the control axes of the lamination molding apparatus 1 areenumerated again. The control axis in the horizontal uniaxial directionof the processing head 21 is set to the X axis, the control axis in thehorizontal uniaxial direction orthogonal to the X axis is set to the Yaxis, the control axis in the vertical uniaxial direction is set to theZ axis, and the control axis in the rotation direction of the spindlehead 211 is set to the R axis. In addition, the control axis in thehorizontal uniaxial direction in which the recoater head 4 moves is setto the S axis. Moreover, the control axis in the vertical uniaxialdirection in which the molding table 33 moves is set to the U axis.Further, the control axes of the pair of galvanometer mirrors 55, 57 areset to the A axis and the B axis respectively.

Next, with reference to FIG. 6, a control system of the laminationmolding apparatus 1 according to this embodiment is described. A CAMdevice 71 generates project files for forming the desiredthree-dimensional object including a main program, a cutting programfile, and a molding program file. The main program is composed by aplurality of program lines, each being allocated a sequence number. Theprogram lines include a sintering instruction for each divided layer ofa specific thickness of the desired three-dimensional object or acutting instruction for cutting each sintered layer. Specificinstructions related to the cutting path of the cutting tool 212 duringend surface cutting or the scanning path of the laser beam L areincluded in the cutting program file or the molding program file.Basically, the cutting path during the end surface cutting included inthe cutting program file is to outwardly add an offset of a radius r ofthe cutting tool 212 to the contour of the irradiation areas β in thedivided layers corresponding to the sintered layers to be cut. However,as described in the following, the cutting path of the cutting tool 212during the upper surface cutting is not included in the cutting programfile, but is generated in each cutting by the numerical control device73. Further, the cutting path refers to a movement track of the centerof the cutting tool 212 during cutting. In addition, the CAM device 71performs interference check of the cutting program file and the moldingprogram file to prevent interference including between the molded objectand the cutting tool.

The numerical control device 73 includes a storage device 731, acomputation device 732, and a memory 733. The storage device 721 storesthe project file sent by the CAM device 71 by means of a removablestorage medium such as a flash memory or through a communications line.The computation device 732 executes various computations related tonumerical control. For example, the computation device 732 analyzes themain program file and the cutting program file, and outputs instructionsignals to control devices 811, 821, 831, 841, 851, and 861 of variousaxes, so that the control devices execute the main program according tothe program lines. In addition, the computation device 732 determineswhether the irradiation areas β in all the divided layers are includedin the molding area α. The memory 733 temporarily stores the mainprogram file and the cutting program file analyzed by the computationdevice 732. The data to be stored includes a maximum value X_(MAX) ofthe X coordinate, a maximum value Y_(MAX) of the Y coordinate, a minimumvalue X_(MIN) of the X coordinate, and a minimum value Y_(MIN) of the Ycoordinate of the molded object. A display device 75 is connected to thenumerical control device 73, and displays a work state of the laminationmolding apparatus 1 or error messages on the screen based on data sentfrom the numerical control device 73.

Based on the analyzed main program file and cutting program file, thenumerical control device 73 sends desired instruction signals to thecontrol devices 811, 821, 831, 841, 851, and 861 of various axes. Thecontrol devices 811, 821, 831, 841, 851, and 861 of various axes senddesired instruction signals to drive current supply devices 812, 822,832, 842, 852, and 862. The drive current supply devices 812, 822, 832,842, 852, and 862 send drive currents corresponding to the instructionsignals to motors 813, 823, 833, 843, 853, and 863 of the axesrespectively. In addition, the motors 813, 823, 833, 843, 853, and 863are under feedback control.

A laser control device 77 is connected to the numerical control device73, receives the molding program file from the numerical control device73, and analyzes the molding program file to generate laser beamirradiation data. Based on the laser beam irradiation data, the lasercontrol device 77 sends desired instruction signals to control devices871 and 881 of various axes. The control devices 871 and 881 of variousaxes send desired instruction signals to drive current supply devices872 and 882. The drive current supply devices 872 and 882 send drivecurrents corresponding to the instruction signals to actuators 873 and883 of the galvanometer mirrors 55 and 57. The galvanometer mirrors 55and 57 achieve desired rotation angles by means of the drive currents,thereby determining the irradiation position of the laser beam L on themolding table 33. Further, the laser control device 77 controls ON/OFFor intensity of the laser beam L emitted by the laser beam source 51. Inaddition, the actuators 873 and 883 are under feedback control.

Here, the method for determining whether the irradiation areas β of alldivided layers are included in the molding area α is described indetail. The determining is performed at least before the forming offirst sintered layer by using the laser beam L starts. In thisembodiment, the determining is performed between the start of themolding, that is, the execution of the program file and the formation ofthe first material powder layer.

First, the computation device 732 finds a maximum value αX_(MAX) of theX coordinate, a maximum value αY_(MAX) of the Y coordinate, a minimumvalue αX_(MIN) of the X coordinate, and a minimum value αY_(MIN) of theY coordinate of the molding area α. The stroke ranges of the laser beamL are set to L_(X) and L_(Y) for the X axis and the Y axis respectivelyon the numerical control device 73. In addition, as described above, thelaser origin O_(L) (X_(L), Y_(L)) is located at the center of themolding area α. The above is expressed by the following formulas.

$\begin{matrix}{{\alpha \; X_{MAX}} = {X_{L} + \frac{L_{X}}{2}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack \\{{\alpha \; Y_{MAX}} = {Y_{L} + \frac{L_{Y}}{2}}} & \lbrack {{Formula}\mspace{14mu} 2} \rbrack \\{{\alpha \; X_{MIN}} = {X_{L} - \frac{L_{X}}{2}}} & \lbrack {{Formula}\mspace{14mu} 3} \rbrack \\{{\alpha \; Y_{MIN}} = {Y_{L} - \frac{L_{Y}}{2}}} & \lbrack {{Formula}\mspace{14mu} 4} \rbrack\end{matrix}$

Next, the computation device 732 is used to find a maximum valueβX_(MAX) of the X coordinate, a maximum value βY_(MAX) of the Ycoordinate, a minimum value βX_(MIN) of the X coordinate, and a minimumvalue βY_(MIN) of the Y coordinate of the irradiation area β. Themaximum value X_(MAX) of the X coordinate, the maximum value Y_(MAX) ofthe Y coordinate, the minimum value X_(MIN) of the X coordinate, and theminimum value Y_(MIN) of the Y coordinate of the molded object arealready known, which may be obtained with reference to data stored inthe memory 733. Besides, the work offset values of the X axis and the Yaxis are X_(W) and Y_(W) respectively. The above is expressed by thefollowing formulas.

βX _(MAX) =X _(MAX) +X _(W)  [Formula 5]

βY _(MAX) =Y _(MAX) +Y _(W)  [Formula 6]

βX _(MIN) =X _(MIN) +X _(W)  [Formula 7]

βY _(MIN) =Y _(MIN) +Y _(W)  [Formula 8]

At this time, when

(αX _(MAX) ≧βX _(MAX))

(αY _(MAX) ≦βY _(MAX))

(αX _(MIN) ≦βX _(MIN))

(αY _(MIN) ≦βY _(MIN))  [Formula 9]

is true, it can be determined that the irradiation areas β of alldivided layers are included in the molding area α. In addition, becausethe cutting path during the end surface cutting is to outwardly add anoffset of a radius r of the cutting tool 212 to the contour of theirradiation areas β in the divided layers, and the interference check isalso performed in the CAM device 71, it can be determined that thescanning path during the end surface cutting is also appropriate. Atthis time, the numerical control device 73 instructs other parts tostart molding.

If Formula 9 is false, it may be known that the irradiation area β of atleast one divided layer exceeds the molding area α. At this time, beforethe sintered layer is formed, the numerical control device 73 sends aninstruction for displaying an error message to the display device 75,reminding an operator of checking whether the project file isappropriate.

As described above, the numerical control device 73 determines, at leastbefore the sintering, whether the irradiation areas β of all dividedlayers are included in the molding area α. The process includes: findingcoordinate values of four points including the maximum value αX_(MAX)and the minimum value αX_(MIN) of the X axis and the maximum valueαY_(MAX) and the minimum value αY_(MIN) of the Y axis of the moldingarea α, finding coordinate values of four points including the maximumvalue βX_(MAX) and the minimum value βX_(MIN) of the X axis and themaximum value βY_(MAX) and the minimum value βY_(MIN) of the Y axis ofthe irradiation area β, and comparing the maximum value αX_(MAX) of theX axis of the molding area α with the maximum value βX_(MAX) of the Xaxis of the irradiation area β, the minimum value αX_(MIN) of the X axisof the molding area α with the minimum value βX_(MIN) of the X axis ofthe irradiation area β, the maximum value αY_(MAX) of the Y axis of themolding area α with the maximum value βY_(MAX) of the Y axis of theirradiation area β, and the minimum value αY_(MIN) of the Y axis of themolding area α with the minimum value βY_(MIN) of the Y axis of theirradiation area β. When the maximum value αX_(MAX) of the X axis of themolding area α is greater than or equal to the maximum value βX_(MAX) ofthe X axis of the irradiation area β, the maximum value αY_(MAX) of theY axis of the molding area α is greater than or equal to the maximumvalue βY_(MAX) of the Y axis of the irradiation area β, the minimumvalue αX_(MIN) of the X axis of the molding area α is smaller than orequal to the minimum value βX_(MIN) of the X axis of the irradiationarea β, and the minimum value αY_(MIN) of the Y axis of the molding areaα is smaller than or equal to the minimum value βY_(MIN) of the Y axisof the irradiation area β, it is determined that the irradiation areas βof all divided layers are included in the molding area α. Therefore, notonly the three-dimensional object can be formed in the molding area αproperly, but also the coordinate values αX_(MAX), αX_(MIN), αY_(MAX),αY_(MIN), βX_(MAX), βX_(MIN), βY_(MAX), and βY_(MIN) can be obtainedeasily from numerical data of the cutting program file or moldingprogram file which is an NC program. In this way, the inclusion statuscan be easily and rapidly determined.

Further, when the lamination molding apparatus 1 includes the cuttingdevice 2 and performs the upper surface cutting, preferably, it isdetermined, at least before the cutting, whether the cutting area δ thatis to be cut by the cutting tool 212 is located in a cuttable area γwhose largest range is an area surrounded by the powder holding wall 35.In this embodiment, the determining is performed right before the uppersurface cutting.

Here, the method for generating a cutting path of the upper surfacecutting is described. The cutting path of the upper surface cutting isset in a manner of covering at least the entire upper surface of thesintered layer or the molding plate 61 to be cut, which, for example, isobtained as follows. As shown in FIG. 7, first, the computation device732 obtains a rectangular area having vertices of (X_(MAX)+X_(W),Y_(MAX)+Y_(W)), (X_(MAX)+X_(W), Y_(MIN)+Y_(W)), (X_(MIN)+X_(W),Y_(MAX)+Y_(W)) and (X_(MIN)+X_(W), W_(MIN)+Y_(W)) with reference to themaximum values and minimum values X_(MAX), Y_(MAX), X_(MIN), and Y_(MIN)of the X axis and Y axis of the molded object (or the molding plate 61when the object to be cut is the molding plate 61, instead of the moldedobject) and the work offset values X_(W) and Y_(W). The maximum valuesand minimum values X_(MAX), Y_(MAX), X_(MIN), and Y_(MIN) and the workoffset values X_(W) and Y_(W) are stored in the memory 733. Then, thecomputation device 732 adds an offset of the radius r of the cuttingtool 212 to the outer side of the rectangular area to obtain a referencearea shown as a dashed line in FIG. 7.

As shown in FIG. 8, the cutting path is a moving path of the cuttingtool 212 when reciprocating movement indicated by the arrows with onevertex of the reference area as a starting point is performed n times soas to cover the reference area. In this embodiment, one reciprocatingmovement consists of a movement from an edge of the reference area tothe opposite edge of the reference area in the +X direction, a movementof a pitch width p in the +Y direction, a movement from an edge of thereference area to the opposite edge of the reference area in the −Xdirection, and a movement of a pitch width p in the +Y direction.Moreover, a pitch width p is a specific value satisfying 0<p≦φ, and φ isthe diameter of the cutting tool 212. Here, n is the smallest naturalnumber satisfying.

$\begin{matrix} {n \geq \frac{( {Y_{MAX} + Y_{W} + r} ) - ( {Y_{MIN} + Y_{W} - r} )}{2\; p}}\Leftrightarrow{n \geq \frac{Y_{MAX} - Y_{MIN} + \phi}{2\; p}}  & \lbrack {{Formula}\mspace{14mu} 10} \rbrack\end{matrix}$

At this time, as shown in FIG. 8, an area formed by outwardly adding anoffset of the radius r of the cutting tool 212 to the outer side of thesmallest rectangular area including the cutting path is the cutting areaδ.

In addition, when the project file is not executed, upper surfacecutting can be performed separately. For example, upper surface cuttingon the molding plate 61 is performed before the molding. At this time,before the upper surface cutting, the maximum values and minimum valuesX_(MAX), Y_(MAX), X_(MIN), and Y_(MIN) of the X axis and Y axis and thework offset values X_(W) and Y_(W) must be input manually in advance.

Next, the method for determining whether the cutting area δ is locatedin the cuttable area γ is described. First, the computation device 732is used to find a maximum value γX_(MAX) of the X coordinate, a maximumvalue γY_(MAX) of the Y coordinate, a minimum value γX_(MIN) of the Xcoordinate, and a minimum value γY_(MIN) of the Y coordinate of thecuttable area γ. The largest range of the cuttable area γ is an areasurrounded by the powder holding wall 35. However, for the purpose ofsafety, the cuttable area γ may also be set to shrink inwardly by aspecific width. In other words, an area obtained by adding an offsetvalue equivalent to a safety width m to the outer side of the moldingarea α may serve as the cuttable area α. Moreover, when the width of theupper wiper 37 is set to M, 0≦m≦M. The above is expressed as thefollowing formulas.

γX _(MAX) =αX _(MAX) +m  [Formula 11]

γY _(MAX) =αY _(MAX) +m  [Formula 12]

γX _(MIN) =αX _(MIN) −m  [Formula 13]

γY _(MIN) =αY _(MIN) −m  [Formula 14]

Next, as described above, the computation device 732 is used to obtainthe cutting path of the upper surface cutting, and to find the maximvalue δX_(MAX) of the X coordinate, the maximum value δY_(MAX) of the Ycoordinate, the minimum value δX_(MIN) of the X coordinate, and theminimum value δY_(MIN) of the Y coordinate of the cutting area δ. Asshown in FIG. 8, the above is expressed as the following formulas.

$\begin{matrix}{{\delta \; X_{MAX}} = {X_{MAX} + X_{W} + \phi}} & \lbrack {{Formula}\mspace{14mu} 15} \rbrack \\{{\delta \; X_{MIN}} = {X_{MIN} + X_{W} - \phi}} & \lbrack {{Formula}\mspace{14mu} 16} \rbrack \\{{\delta \; Y_{MIN}} = {Y_{MIN} + Y_{W} - \phi}} & \lbrack {{Formula}\mspace{14mu} 17} \rbrack \\\begin{matrix}{{\delta \; Y_{MAX}} = {{\delta \; Y_{MIN}} + r + {2\; {pn}} + r}} \\{= {Y_{MIN} + Y_{W} + {2\; {pn}}}}\end{matrix} & \lbrack {{Formula}\mspace{14mu} 18} \rbrack\end{matrix}$

At this time, when

(γX _(MAX) ≧δX _(MAX))

(γY _(MAX) ≧δY _(MAX))

(γX _(MIN) ≦δX _(MIN))

(γY _(MIN) ≦δY _(MIN))  [Formula 19]

is true, it can be determined that the cutting area δ is included in thecuttable area α. At this time, the numerical control device 73 instructsother parts to start the upper surface cutting.

If Formula 19 is false, it is known that the cutting area δ exceeds thecuttable area γ. At this time, before the upper surface cutting, thenumerical control device 73 sends an instruction for displaying an errormessage to the display device 75, reminding an operator of checkingwhether the project file or setting is appropriate.

As described above, the numerical control device 73 determines, at leastbefore the cutting, whether the cutting area δ is included in thecuttable area γ. The process includes finding coordinate values of fourpoints including the maximum value γX_(MAX) and the minimum valueγX_(MIN) of the X axis and the maximum value γY_(MAX) and the minimumvalue γY_(MIN) of the Y axis of the cuttable area γ, finding coordinatevalues of the maximum value δX_(MAX) and the minimum value δX_(MIN) ofthe X axis and the maximum value δY_(MAX) and the minimum value δY_(MIN)of the Y axis of the cutting area δ, and comparing the maximum valueγX_(MAX) of the X axis of the cuttable area γ with the maximum valueδX_(MAX) of the X axis of the cutting area δ, the minimum value γX_(MIN)of the X axis of the cuttable area γ with the minimum value δX_(MIN) ofthe X axis of the cutting area δ, the maximum value γY_(MAX) of the Yaxis of the cuttable area γ with the maximum value δY_(MAX) of the Yaxis of the cutting area δ, and the minimum value γY_(MIN) of the Y axisof the cuttable area γ with the minimum value δY_(MIN) of the Y axis ofthe cutting area δ. When the maximum value γX_(MAX) of the X axis of thecuttable area γ is greater than or equal to the maximum value δX_(MAX)of the X axis of the cutting area δ, the maximum value γY_(MAX) of the Yaxis of the cuttable area γ is greater than or equal to the maximumvalue δY_(MAX) of the Y axis of the cutting area δ, the minimum valueγX_(MIN) of the X axis of the cuttable area γ is smaller than or equalto the minimum value δX_(MIN) of the X axis of the cutting area δ, andthe minimum value γY_(MIN) of the Y axis of the cuttable area γ issmaller than or equal to the minimum value δY_(MIN) of the Y axis of thecutting area δ, it is determined that the cutting area δ is included inthe cuttable area γ. Therefore, not only cutting can be performed in thecuttable area γ properly, but also the coordinate values γX_(MAX),γX_(MIN), γY_(MAX), γY_(MIN), δX_(MAX), δX_(MIN), δY_(MAX), and δY_(MIN)can be obtained easily from numerical data of the cutting program fileor molding program file which is an NC program. In this way, theinclusion status can be easily and rapidly determined.

In this embodiment, the position of the cutting area δ is determinedright before the upper surface cutting, which, however, may also bedetermined at other timing. For example, the position of the cuttingarea δ related to the upper surface cutting included in the program fileis determined at the same time as the position of the irradiation area βis determined; or the position of the cutting area δ related to theupper surface cutting which is performed separately when the programfile is not executed is determined separately right before the uppersurface cutting. However, it is more appropriate to determine theposition of the cutting area δ right before the upper surface cutting isto be performed, because this can adapt to the situation when thecutting path is changed during the execution of the program file.

The present invention is not limited to the configurations in theembodiments illustrated by the drawings as the examples describedherein, but can have various modifications or applications withoutdeparting from the scope of the technical concept of the presentinvention.

What is claimed is:
 1. A lamination molding apparatus, comprising: achamber, covering at least a molding area which is the maximum range inwhich a three-dimensional object can be produced; a molding table,disposed in the molding area in the chamber, on which material powderlayers are formed by uniformly spread material powder for each of aplurality of divided layers, wherein the divided layers are obtained bydividing a desired three-dimensional object for each of a specificthickness; a powder holding wall, surrounding the molding table andholding the material powder supplied onto the molding table; a laserirradiation device, forming sintered layers by irradiating laser beam onspecific irradiation areas defined by the contour shape of the dividedlayers on the material powder layers; and a numerical control device,determining, at least before sintering, whether the irradiation areas ofall the divided layers are included in the molding area.
 2. Thelamination molding apparatus according to claim 1, wherein the numericalcontrol device determines, at least before the sintering, whether theirradiation areas of all the divided layers are included in the moldingarea by: finding coordinate values of four points in a laser coordinatesystem of the laser irradiation device, wherein a center of the moldingarea is an origin of the laser coordinate system, and the four pointsare a maximum value and a minimum value of an X axis of a control axisin a horizontal uniaxial direction of the molding area and a maximumvalue and a minimum value of a Y axis of the control axis in ahorizontal uniaxial direction that is orthogonal to the X axis; findingcoordinate values of four points of the irradiation area, wherein thefour points are a maximum value and a minimum value of the X axis and amaximum value and a minimum value of the Y axis; comparing the maximumvalue of the X axis of the molding area with the maximum value of the Xaxis of the irradiation area, the minimum value of the X axis of themolding area with the minimum value of the X axis of the irradiationarea, the maximum value of the Y axis of the molding area with themaximum value of the Y axis of the irradiation area, and the minimumvalue of the Y axis of the molding area with the minimum value of the Yaxis of the irradiation area; and determining that the irradiation areaof all the divided layers is included in the molding area when themaximum value of the X axis of the molding area is greater than or equalto the maximum value of the X axis of the irradiation area, the maximumvalue of the Y axis of the molding area is greater than or equal to themaximum value of the Y axis of the irradiation area, the minimum valueof the X axis of the molding area is smaller than or equal to theminimum value of the X axis of the irradiation area, and the minimumvalue of the Y axis of the molding area is smaller than or equal to theminimum value of the Y axis of the irradiation area.
 3. The laminationmolding apparatus according to claim 1, further comprising a cuttingdevice, wherein the cutting device comprises a cutting tool capable ofmoving inside the chamber and cutting upper surfaces of the sinteredlayers or an upper surface of a molding plate disposed on the moldingtable; and the numerical control device determines, at least before thecutting, whether a cutting area to be cut by the cutting tool isincluded in a cuttable area whose largest range is an area surrounded bythe powder holding wall.
 4. The lamination molding apparatus accordingto claim 3, wherein the numerical control device determines, at leastbefore the cutting, whether the cutting area is included in the cuttablearea by: finding coordinate values of four points of the cuttable area,wherein the four points are a maximum value and a minimum value of the Xaxis and a maximum value and a minimum value of the Y axis; findingcoordinate values of four points of the cutting area, wherein the fourpoints are a maximum value and a minimum value of the X axis and amaximum value and a minimum value of the Y axis; comparing the maximumvalue of the X axis of the cuttable area with the maximum value of the Xaxis of the cutting area, the minimum value of the X axis of thecuttable area with the minimum value of the X axis of the cutting area,the maximum value of the Y axis of the cuttable area with the maximumvalue of the Y axis of the cutting area, and the minimum value of the Yaxis of the cuttable area with the minimum value of the Y axis of thecutting area; and determining that the cutting area is included in thecuttable area when the maximum value of the X axis of the cuttable areais greater than or equal to the maximum value of the X axis of thecutting area, the maximum value of the Y axis of the cuttable area isgreater than or equal to the maximum value of the Y axis of the cuttingarea, the minimum value of the X axis of the cuttable area is smallerthan or equal to the minimum value of the X axis of the cutting area,and the minimum value of the Y axis of the cuttable area is smaller thanor equal to the minimum value of the Y axis of the cutting area.